Just a gentle correction to what SimonGent says.
The NIP does not have to be served upon the registered owner within 14 days. In fact it does not have to be served at all for the matter to continue. The legislation says that it must be posted so that in normal circumstances it would reach the address of the registered keeper within 14 days.
If it does not arrive, or if the registered keeper ignores it, the matter will still proceed. The speeding charge will be dropped and the CPS will issue a summons under Section 172 of the Road Traffic Act which requires the registered keeper to provide details of the driver at the time of the alleged offence.
If this summons is ignored the matter will be heard in absence by the magistrates. (The usual fine for this offence is about �350, three penalty points, plus �45 costs). If the summons is answered it will be for the registered keeper to persuade the magistrates that the original paperwork (the NIP etc.) was not received. If he manages to do this the CPS might be minded to revert to the original speeding offence. However, this is a matter for them to decide and they will take a view on where their best chance of a successful prosecution lies.
I know this all sounds a bit pedantic, but it�s important to know all this if you are looking for potential loopholes. The matter will only be dropped entirely if the magistrates are not convinced that the original NIP was posted in time to reach the recipient within the 14 day deadline.